[yorwba]

In this case, the lookup table is used for popcount, and there's a comment in the Z80 assembly that says "One lookup vs eight bit tests." If the code could make use of a hardware popcount instruction, the lookup table would lose, but if that isn't available, a 256-byte lookup table could be faster. So it's less "lookup tables are always faster" and more "lookup tables can be faster, this is one such case."

[ooisee]

probably fastest popcount in z80 that does not use aligned table, would be shift A through flag, then conditional INC C, unrolled, still slower than ld l,a: ld b,(hl).